ESTIMATIOE OF THE RATE OF SDIMETATIOE IN RESERVOIR
by
JUMSAK TEJASEN
A THESIS
submitted to
OREGON STATE UN IVERSITY
in partial fulfillment of the requirements for the
degree of
MASTER OF SCIENCE
June 1962
APPROVED:
Associate Professor of Civil Fgineerir, In Charge of Major
Head of )epartmerit of Civil &ïgineering
Chairman of School Graduate Committee
Dean of Graduate School
Date thesis is presented December 15, 1961
Typed by Verna Anglernier
ACK1 OWIDGEMENTS
The author wishes to express his sincere gratitude
to Dr. Roy Shoemaker of the CIVIl igineering Departnnt
of Oregon State University, for bis valuable advice,
patient understendig, and timu1ating consultation, in
rnakiig this thesis work possible.
Appreciation is also extended to his ror»rnrìate,
r. i1red Stover, who was very helpful in his corrections
and sugç;ostions in the use of the EigUsh language.
TABLE OF CONTETS
Page
INTRODUCTI . . . . . . , . . . , . . , , i
Objective . . . . . s . . . . . . . . . . . i
Purpose of the Reservoir . . . . . . . . . . . 2
The í:robii and the SigilficanCe of Feservo1r I- ed1rientati1 . e . . . . . . . . . . . . 3
FUN DA TAL ThEORY OF SEDIMENTATIO] . . . . . . . . 5
Sedimentation Processes . . . . . . . . . . . 5
F ai i Vel ocit y . . . . . . . . . . . , . . . . O
Stokea's law . . . . . . , , , 3
Fail of particles outside the ranLe of Stokes'siaw .. .. .. . .... . .. 10
MoveznentofSedlxnent . . . . . . . . . . . . . 13
Origin and Nature of Silt . . . . . . . . . . . 16
METHOD OF ESTIMATING THE RATE OF SEDIMFTATION IN RESEBVOIR . . . . . . . . . . . . . . . . . . . 18
Previous Studies of Rates of Sedimentation . . , 18
Historical . . . . . . . . . . . . . . . 18
Factors t.iat influence sedimentation in r esorvoir . . . . . . . . . . . . . . . 19
The Proposed Method . . . . . . . . . . . . . . 25
SUGE8TIO.S FOR FUTURE STUDY . . . . . . . . . . . . 32
DISCTJsSIoi:0FRESuLT5.,...,.......,.. 33
CCLUS I ci S . . . . . . . . . . . . . . . . . . . 34
BIBLIOGP . . . . . . . . . . . . . . . 36
AP:EN DIX . e e e e e e e e e e e i e e e e . e e 38
LIST OF FIGURES
Figure Pate i Settling of particles . . . . . . . . . . . . 6
2 Relation of the Rejno1ds number to resl.stvyice coefficient (1, p. 781) . . . . . . . . . . 12
3 Sediment accumulation in a typical reservoir 15
4 Trap efficiency of typical reservoirs . . . . 21
ESTIMATI OF THE RATE OF SEDflTETATIO1 fl RESERVOIR
IN TRODUC TI ON
Objective
rjhe loss of use of a good dam site eeause the
reservoir fills with slit is a serious economic problem.
Good darn sites are scarce, and the first site elected arid
used may exhaust the opportunity for economic development
or. a stream or in an area. If the reservoir is destroyed
by siltln;, the possibility for building replacement
projects are usually limited or nor-existent.
rethods of estimating the rate of sedimentation. in a
proposed reservoir are desirable, technically and econ-
omicafly, arid may be approached at present from several ways.
The method proposed in this thesis is to be used in
estimating the future percentage loss of total reservoir storage through the use of past records of storage loss.
neo show that this method will te practicable and close enough for estimating, two general methods will be
used for comparison.
Accordiig to time and materials available the writer
2
will select representative records of sedimentation of
three reservoirs of different sizes. The three methods
mentioned above will be used in analyzing each of the
three reservoirs.
The results from this analysis also will be shown in
comparison with records o.E the actual rate of sedimenta-
tion both in graph end tabular form.
Purpose of the Reservoir
While the primary purpose of most reservoirs is to
provide storage, their most important physical character- istic is storage capacity. The capacity of a reservoir
of regular shape caí: be computed wi th the formulas for the
volumes of solids. Capacity of reservoirs on xìatural
sites must usually be determined from topographic surveys.
If a long-time record of annual total discharges from
the stream is available, the storage required to yield the
average flow, each year, is obtained by computing the
cumulative sums of the departures of the annual totals
from the mean annual total discharge. The range from the maximum to the minimum of these cumulative totals is taken
as the required storage.
In the design of many reservoirs, provision is made
for dead storage and live storage. The former is con-
sidered to provide space for the deposition of sediment
3
for a considerable period of years. The ultimate destiny
of all reservoirs is to be filled with sediment. If the
sediment ini'low is large compared with the reservoir
capacity, the useful life of the reservoir may be very
short. Reservoir planning must include consideration of
the probable rate of sedimentation in order to determine
whether the useful life of the proposed reservoir will be
sufficient to warrant its construction.
The Problem and the S1iificance of Reservoir Sedimentation
Sedimentation in reservoirs has become increasingly
important because of the increasing number of dams and
reservoirs bu1t and continuing to be built. Such roser-
voirs may be so affected by sedimentation that one or more
of their major purposes, such as flood control, navigation,
irrigation, water supply, hydroelectric-power production
may be seriously curtailed or even cancelled. Once sediment has boon deposited in a reservoir,
disposal is extremely difficult and practically impossible.
In. isolaied nases, density currents have carried some silt
thouì a reservoir. However, the effect of density cur-
rent flow on the amount of sediment deposited within the
reservoir is necessarily small. On some projects, it is possible to carry eHt throui a dam by means of sluices
through the structure. Ordinarily, however, this is not
feasible, because to reduce materially the sediment con-
tent of a reservoir would require a long period of sluic-
ing auring which the reservoir would be out of use.
Dredging in a few special cases may be resorted to, but
this method is not generally applicable (11, p. 361).
5
FUNDAMENTAL THEORY OF SEDIMENTATION
Sedimentation Processes
Flowing water has the power to transport 1ar:.e quan-
titioS Oi fine1 divided material as a suspended load and
also to drag other materials along its bed. The hiLer
the velocity and the more turbulent tue stream, the
greater the proportion of suspended load it s capable of
carrying. hen velociti es slacken this material settles
and the bed-load movennt is arrested. Material x'emains
in suspension by reason of the vertical components of cur-
rents and eudios within the water prism.
Whore the reservoir capacity Is small compared to the
annual inflow, it may happen that a consIderable part of
the suspended load is carried through the reservoir and
only the bed load is deposited. This is evidenced on many
streams where the space above dams has been completely
filled with coarse travel and cobbles.
The settling path of a particle is determined by the
vector sum of Its f&1 velocity and the flow velocity.
If V the discharge per unit of reservoir surface
area
--.- V,
pa1k o V
Figure 1. Settling of particles
7
Particles having settling velocity equal to or
;reater than V0, will all settle out. In estimatIng the
siltlng action in reservors, therefore, the Call velocity
is one of the most siificant factors which must be
considered.
Fall Velocity
The velocity of fall of any particle within a fluid
depends upon many variables. The principal ones are the
size, shape, and specific ;ravity of the particle and the
viscosity of the fluid.
Stokes's law
If a sin2;le sphere is allowed to fall through a
liquid which is of idefin!te extent, its velocity will increase rapidly at first under the acceleration of gray-
ity; however, a constant terrnia]. velocity is practically reached within a few seconds and is maintained ndefinite-
ly, as long as conditions are not changed.
sw D2 (9, p. 31 and 32)
where and ' aro the unit weights of sphere and liquid, respectively, )A is the viscosity of the liquid, and D is the diameter of the sphere.
Stokes's law Is applicable for spheres between about
0.2 and 0.0002 inn in diameter Lolling thr.igh water. It C, not be used when the spheres are larger tEar 0.2 nun;
because turbulence will occur and the assumptions that
"constant velocity is practically maintained indefinitely, as long as condi tions are not changed" are invalidated.
In turbulent flow the direction of the current of a
given point channes rapidly and haphazardly. Although
the flow at the point has a general forward notion, In a
short space of time small area of flow, or eddies, fluc- tuate In horizontal and vertical directions. These fluc- tuations are Irregular and spontaneous and do not follow any definite sequence.
It has been established by measurements made at the U.S. Waterways }xperiment Station that flow will be
turbulent if 4,000 (2, p. 1140)
V
where V mean velocity, fps
R hydraulic radius, ft V = kinematic viscosity, ft squared per sec
For water at 70 F the kinematic viscosity is approximately
0.00001.
It defines a condit..on below which all turbulence entering the flow from any source will eventually be
damped out by viscosity. ruhe turbulence theory offers an explanation of sus-
pended sediment transportation. Accordin to this theory, there is a random, irregular transfer of energy from the fluid to silt, and from silt particle to eilt particle. The energy transferred is the difference between forces that buoy the particles and those that tend to cause them
lo
settle (4, p. 58).
The shape of the silt partIcle has an important bear- Ing a whether it remains in suspeision or settles to th bottom. The finer the mate:Ial the slower it settles. Any Irregular particle should settle more slowly than a
sphere of equal volume and specific gravity, because the
irregular particle presents a greater surface area arid
hence has a greater resistance to motion than the sphere.
Fall of particles outside the range of Stokes's law
Resisiig force CDAV2/22
Gravity force 4/311 r3
where CD coefficient of resistance dependent upon the
interrelation of the properties of particle and fluid
A cross-section area of the paricle V = fall velocity of the particle
1D1 and2 density of particle and fluid, respectively g acceleration due to gravity
For a constant rate or fall i CDAV2/92 = 4/311r3(/0i_iO2)
CD : 8g (/1-,P2)r 3 12V (10, p. 38)
The Reynolds number, R 2.rvf2
11
Corresponding values or CD d R have been calculated
for 3vai conditions of particle and fluid, where fall
velocities have been dotoxiiined oxperimentally in air as
well as in a variety of liquids, d are shown plotted on
logarithmic scales in Figure 2
4 Io
3
(J
I- 2
u.1
o L)
L)
'I-)
UI
12
1111 cD..
B(cP-p2)r R 2ryR2
3e2v1___ -
I I
(T.UE REI ATON FOR SPHERE
0M STOKESSLfrW OBTM ED BYEXPERIMENT
\ -
-0Tr---,0I I IO
IO LO3 o'
REYNOLDS NUMBER R
Figure 2. Re1at1a of the Reino1ds number to resistance coefficient (1, p. 781)
13
Movement of Sediment
The sedimenb produced by erosion finds itas way to the
reservoir by movement in suspension, and movement as bed
load. The former accounts for the transport of mozt of
the finer sedir.erït, whereas the coarser sands and ¿ravels,
and boulders, are moved by rolling along the bed of the
s tream.
Vaen a stream carrying a load of sediment into a
reservoir meets the det waters of the reservoirs its velocity is destroyed and the degree of turbulent rXiITLg
is minimized. Its load of silt is deposited, forming a
delta. This delta consists of the suspended load of the
stream, sorted from coarse to fine. The finer particles are distributed farther out in the reservoir. The dIffer- once in specific gravity be bween the suspension and the
clear water into which it flows tends to minimize the
turbulent mixing, with the result that after only partial dilution the suspension forms a gravity under-flow or
density current. This density current has a greater density than does the water in the reservoir; if it is allowed to staate, the silt will e deposited. Other-
Wi SC , the densi ty current may carxy the finely di vided
suspended matter through the reservoir with a minimum of
silting, provided that outlets are provided at such
14
elevations as will allow this to occu.r. In the caso of
contact WI th water containing a high concentrat on of
dissolved sa1t, the stroi ,' sodium Ions of the chlorIdes
are exchanged with the calcium and maiesIum ions of the
clays or colloidal materials, thIch thereupon lose tieIr
charge, attract one another, d f oxìi relatively large
fioca. Through such flocculation, larger velocities of
fall than those corresponding to the individual particle sizes will result (1, p. 782). Thus, if this density
current could be controlled, much of the sediment entering
a reservoir ccild be voided before deposition.
The distribution of sediment In a reservoir depends
on the shape of the basin. If the reservoir is regular
in shape, deposits from suspension will be distributed
quite uniformly along its axis, decreasing in depth with
distance above the dam. If the reservoir Is irregular, there may be marked Irregularity in the depths of the
bottom-set beds.
ç- ---- --..;--
-.-% I \ DELTA CLEAR WATER \
LAKE \'-SLUICEWAYS
DENSiTY
FINE SEDIMENTS
Figure 3. Sediment accumulation in a typical reservoir
H Cn
16
Origin and Nature of Silt
The charac er of the drainage area and i ts voce tal cOvorin are olï important facors. If the rocks of the
area are scdlrnontaries, such as sandstone, clajs, and
sbales, disintegratci processes produce 1are quantities of fino soils. Silt deposIted in a reservoir varios
great1r in weicht and voluiie, depending on its source, the
depth of deposition, and the degree of submersion or ex-
posure Moasurexnen ts of the average weiLht of dna d si lt per cubic feet of material in placo, taken at several
reservoirs, vary from 18 to 37 Ib per ou ft, when the
deposited material has been wider water at all times, to
85 or 100 lb per ou Lt, or even higher, at locations where
the deposits were subject to alternate wetting and drying.
These values differing in each case not only due to dif-
ferent nonditions of operation oí' the reservoirs, but also
to the varying gradations and sizes of the particles of
which the deposits are composed.
Due to varying characteristics of 1are drainage
areas and the varying conditions under thich reservoirs
are operated, it has been impossible to set a definite
value for the dry weit of the deposited s.lt. However,
after considering all factors entering into the problems,
including the fact that an indeterminable quantity of
17
voetabio matter depoa!ii a10 arid lasts indefinitely, a
value of 70 ib per cu ft of material in place ias been
choeen as an average u1tmate figure for reservoirs in which silt depos±ts are subject to alterLate weiting and
drying (7, p. 253).
Reduction in the 2tcrae capacities 01' reservoirs is likely to be caused by deposition of silt derived from
theIr catchment areas. The amount of silt deposited depends upon the extent of catchment area, the rature ol'
surface soils, c1matic conditions and the slope of the country. Soils wi1ch disintex'ate under the action o' the weather or are soluble, are the most silt-producing. The
climatic cc1ditoL1 leading to the production of silt are
trG.3t, Intenso heat, dryness, and violent downpour ol rain scouring the rod. More silt is produced by steep slopes, are surfaces amid soluble soils and ss silt bj ent1e slot'es, surfaces covered y vegetation, and hard
or insoluble so1.ls. In the tropics most of the silt is washed down by the first heavy stors which carry off materials 1ooso:ed by a long period of draugbt with a high temperature.
lo
METHOD OF FSTIMATflT THE RATE OF SEDIMENTATION IN ÏSE1IVOIR
Previous St';.dles of Rates of Sedirnertatlon
Historical
Studies of' storage reservoIrs in the histor,r by the
Soli Coxservaton service of the U.S. Department of
Agriculture. Investigations lead engineers to believe
that sedimentation will limit tUe usefulness of .ost of
them to loss thsr. 200 years (15, p. 1047).
In estimttlrg the rates of sediment products and
deposltios ir any reservoir, few eneralizations cr.n be
applied. The best basis for such an estintte would be
1°L tern records of suspended-load aiid bed-load measure-
monts made at, or near, the reservoir site.
At this potctt the engIneer will have to c1etermie how
xiìuch of the load vïill p&s through the reservoir and how
much will be deposited in it. Depending on the size and
the operating conditions of the proposed reservoir, some
part of the sediment load may be transported through the basin in tUe form of a density current and may be dis- charged over the spiliway or through the outlet rks. At present the lack of adequate data makes such a
determination very difficult.
19
Factors that influence sedimentation in reservoir
The rate at which silt accumulates in a reservoir is a function of many independent and interrelated variables. Some of these factors rriay be listed as follows:
1. The a:'ea and topography of the watershed, 2. The character of the soil and vegetation i the
catcbznent area,
3. The rate and amount of runoff, 4. The rate and amount of ralnf all, 5. Shape of the reservoir, 6. The ratio of the reservoir capacity to the
watershed area, and
7. The method of reservoir operation. It must be recognized, however, that there can be no
clear-cut approach to the solution of rates of sedimerta- tior problems of any iver reservoir. So many factors are involved, and such an infinite combination of those factors exists, that each reservoir presents a special problem that must be studied in detail. In this connection the wrIter will present soc ethods for estimating rates of sedimen- tation in reservoirs with discussions and comparison of
some of them as follows.
The rate of siltIng of an impoundLg reservoir hay be
expressed by the equation
20
CL EQ8 (1, p. 826) C
CL = annual siltin rate or capacity loss, in per cent
per year
E = trap efficiency or incoming sediment trapped, in
per cent = arir.ual net sediment production from the draixa;e
arca (sediment discharge into the reservoir), in
acre-feet per year
C original reservoir stora,e capacity, in acre-feet. The trap efficiency E depends primarily upon the
sediment-load characteristics and the detention timo of
the inflow.
21
f- z '-I
'-I
L4
'a Q- A-
o' f-
f-
La
14
o 26 50 75 lOO 125 ISO 175 200 225 250
RESERVOIR STORE,E CP¼PPC.ITY C/j CREF PER SQ.MILE 0F WktERSI4ED &EP
Figure 4. Trap efficiency or typical reservoirs
Fivelope curves enclosing the data in Figure 4 may
be defined by an equation of the form
i
1+kc/ (2)
22
value of the coefficient k from 0.046 for the lower curve
to 1.00 for the upper curve.
middle curve is 0.1. The coefficient for the
Values of k tend toward that of the upper curve for reservoirs (1) in regions of smaller and more variable
runoff, (2) hoso length and shape tend to increase the
detention time of inflow, (3) where the sediment load is
mainly coarse or highly coagulated, and (4) where outlets
and operation practice are such as to release little water
from tue bottom of the dam and to hold back and store most
of the flood flows.
Witzig (14, p. 1061) has attempted to correlate the
reservoir capacity-watershed ratio to annual sediment
accumulation by making a logarithmic plot of these varia-
bies from data available from 19 reservoirs in the South-
eastern States of Alabama, Georgia, Virginia, Maryland,
and Lorth and South Carolina. By drawing envelope curves tiby eye" to bound the data represen ting severa]. geograph-
cal regions, he obtained a generalized equation of the
following form:
1 SR I(SR)°83 (3) (15, p. 1061)
23
in which tSR is the annual si1ti: rate in acre-ft per
sq. mile 01' drainage area, I denotes Lhe coefficient,
termed "regional 1ndex', and S refers to the original
storage in acre-ft per sq. mile of drainage area.
His re.onal index, ranges from a lower limit of
0.003 or to an upper limit of 0.0375. According to this
relationship, the rate of sediment accumulation may differ between two reservoirs of similar capacity and watershed
area, approximately, by a factor of ten.
Another analysis to determine the relationship of the
reservoir capacity watershed ratio to the rate of sediment
accumulation tas macle by Gottschalk (3, p. 8). The study
was made at the request of Soil Conservation Service
regional officials at Lincoln, Nebraska, to furnish a
basis for estimating maintenance cos ta on 43 government-
owned reservoirs and stock ponds. The formula developed
was:
S 0.00522C.0.0027 + 0.268fl - 1.7974 (4) (3, p.8)
whore S = Total sediment accumulation, in acre-feet
C Capacity f the pond or reservoir, in
acre-feet
A et draina;e area, in acres
T = Age, in years
24
T1is formula was used to computo the probable rate of s1tin of all the ponds and reservoirs on which no
surveys were made. It is believed that this foznu1a will be useful in the areas where the atershed and iservoir factors are the same factors or similar to the watershed and reservoir factors where this formula was developed.
25
rojsed othod
The rate st which ì:!1t accumulatea in a re8rvo1r i
a function ot many variab18, nch us: the area nd
topoj:Dap or the atersed, the character of the soll and
vegetation On the catohmert are, the shape of the reger-
voir, the method of rcservo.r opratìon1 and the rate and
amoiant or rorr. iowever, 1Í tio avera.e ar'ow.t of suz-
pended material entozinj a ¿iv&- reiervo:tr 1 cotant
ever a 1oig period of t1ne, lt Is tho optr10 of tIi writer
that these varab1es etui be ellxnlnated irom the s1t1n;
rato prob1en. y o1iirating these variablea, the aedi-
mertaton rate will depend rnai:ly on the reservoir capacity.
shall asaurne that the amount of sediment depo8i Led :n
a re8ervoir Will he proportional to te roaorvoir capacity.
Tho following cthod ii proposed to be used ií eatirnati
the userul life of a reerv1r.
In tii method, writcr has found lt more cork-
veniet to use porceta,o loss rather thai actual amounts
of sediment and etorae capacity. fast records of storage
loss will he used to tstimate the futuro percentaLe 1os
of total reservoir storage. The eprosslo will be
described as follows:
2G
Lot i:1t al stcrae capacity 100
: Avorao an.ual storae 10 pErcent
a Total s torao 1oìc percent in r
i atora:e loss percent QX
2 years, stora,.e loss percent QX X(QQX)
2Q.X -
= Q(2x..'X2)
s
3 yet%r, storage loas percent * 2QXcX2.X[Q..(2x_Q)(2)]
a 2QX-QX2..'2Q)(2.QX3
e
e
IlL thO sae way, L Q1..(1.uì.X)i]
Swmnarv of reservoir sedirientatiori
Reservoir, Stream, Nearest Town
Initial Av. Total L)rainage Initial capacity Date Length Av. annual annual percenl Av. area in capacity watershed of of sediment storae loss to annual
square mile ratio survey record accurnul. loss date of runoff
n Acre-ft/ Acre-ft Acre4't,T percent survey rotai ret Acre-ft sq. mi1 yrs sq.e Acre-ft
Ococe io. 3 (4, p. 54), Ocooe Rivercktown 496 263 12,002 24.2 July 45 2.9 1,130 2.293 4.22 16.093 6303
11,255 ov 46 4.2 1,120 2.259 4.15 21.316 73019 10,391 Aug 48 6.0 1,060 2.129 3.92 27.356 75795 ?,849 Aug 50 0.0 920 1.856 3.41 31.145 8l055
ilales Bar (4, p. 57), Tennessee River, Jasper
21,790 990 160,850 7.41 Oct 30 17.0 33,600 1.541 0.95 16.137 7ßfl,594 154,200 Oct 35 22.0 33,100 1.520 0.69 19.604 26ßU25 154,084 Oct 40 27.0 25,800 1.165 0.73 19.664 28679 153,045 July 47 33.7 21,400 0.975 0.6 20.206 2EOO26
Conchas (8, p. 43), Canadian River, iìewkirk
7,350 6,950 599,172 82 ìay 40 1.4 1,000 0.144 0.17 0.23 585,112 June 42 3.4 4,710 0.677 0.78 2.66 436,485 576,756 Oct 44 5.7 4,280 0.615 0.71 4.05 381,919 566,163 Feb 49 10.1 3,460 0.498 0.58 5.81 2636
t3
Comparison ol' the results Length Total storage loss percents
Reservoir Actual Proposed Witzig's Gott.'s Record record method method rnethod yrs.
Ocoee Io. 3 2.9 16.093 - - -
4.2 21.316 16.8 7.6 9.0
6.0 27.356 22.4 10.9 9.02
0.0 31.145 29.2 14.5 9.03
hales Bar 17.0 16.137 - - -
22.0 19.604 19.16 15.65 6.3
27.0 19.664 23.00 19.2 6.3
33.7 20.206 27.80 24.0 6.3
Conchas 1.4 0.23 - - -
3.4 2.66 0.60 3.16 7.22 r r A (IZ i (\Z J. I ì. ) ¡
10.1 5.8]. 1.85 9.3 7.23
Gottschalk' s me thod
Graph illustrating total storage loss in percents
Ocoee No. 3 Reservoir
Graph illustrating total storage loss in percents
Hales Bar Reservoir
Graph illustrating total storage loss in percents
Conchas Reservoir
SUGGESTICNS FOR FUTURE STUDY
It i apparent that aternpts to relato the rate of
sedimentation ir reservoiis leave much o be desired.
It i su:ested iat further stud' Include the £ol1owin:
1. Clasificatior of reservoirs accoiin., to srape
as thic factor ma affect deposition;
2. The relatioflship between the reservoir capity the .serched area;
3. The effect o averae annual ruriof f end annual
peak fl.oda o the rate of silt accumulation.
The need i& apparent for more accurate methods of
predictiui aedintation rate in existin. reservoirs.
Also, methods WhICh ello closer estimation cf the axnount
of dead stora required In Lesi.n of a biven reservoir
will be very useful for economic development or a stream
or i nr area.
33
DISCîJSIO: OF RISTJ TS
The reu1ta snow that Gotteha'8 and 'itzig's £orriu1as
wb.ich oro developed 1z'om tho particular areas can not be
applied to compute the probable rate o' i1ting In enerai.
They Tt.1i be useftil only In adjacet areas whore the watcx'-
shod tnd reervo1r factors re the anio. The difference
between the results o1 comutat1orì from these £oruias arid
the actual record llave been shown on the graphs, and as
ldicted, the dlscxepa.cy iLcrea;es wi th the lex.;;th of
po rl od corks Id cred A t the same t l'ne, the results of the
writer's proposed method seem to be closer to the actual
record nnd more useful estiiat1or of the rate of sedI
mcntatior i:,. reservo:r.
CoiCLUsIc?S
Thia ana1ysi indlcats that the rate at which aflt
acouu1tos in a reservo.r Is a furctton of nany thdepori.
dent variables. o manr factors aro ivo1ved, aLad zmch ari
tnfi1te cab1nat.ton of those actor8 exists, that each
reservoir prea&its zipeclai problem which ruzt be studied
as a ptu'ticular caso. There will be :io clear-cut approach
to tbe solution of the prob1en of the rate :: sed1iientat1or
in any ;4von re2ervoir. :owevcr, if the .vera&;e îount of
suspended material entering a ive reservoir is constat
over a 1otí:; period of time, we ci asae that the nua1
vo1uuie of edire;t deposited is d1reot1 proportioraa.1 to
the reservoir capacity. 'iho rete of odiiietat1on ir the
future caz be estiaLated satisfactorily by ua1n o:dy the
auount of anua1 por centa;o loas capaci r id oriine.
storage capacity. owovcr, the accuracy of the prediction
of thie rrethod 1.11 be inproved as niore recorda of sedi-
tentation are ou ;ained.
Ihe two :e.oral rnthode ich are shown in this
thesis consider he nual rato o sedirneut accurnulat10
as a £uuction of the watershed area and capacity o roser-
voir. e ithod of the writer, however, usos the w].:ual
rate of sediment aceumulatiGb as a fuct1on of the reser-
voir capacIty only. The i'esults of a corpariso: ' etween
35
the above methods arid the actual dala sbow that the
writer's proposed method seems to be closer to the actual
records, srid thus more uerul in estimatin the rate of
sedimcntatior. in a reservoir.
I t i pp are rit from the re sul ts shown in graphs,
pagos 29, 30 arid 31, that none of the methods used would
be satisfactory for estimation of the useful lives of
reservoirs, Large reservoirs in their early years have
the abi li ty to settle out vi rtuall y the en tire infi owl ng
sediment load, but with the passage of timo the size of
the detention basin available becomes smaller and smaller
until eventually a major portion of the inflowing sediment
may be carried past the reservoir.
36
BIBLI OGHA P}IY
,i.. Brown, C*z'l B. edimnt transportatic. Th e*ring nydrau11c8 Froceed1n of the i'ourth H1drwflica Conference, Iowa Inetitute of iydrau1- ic hcaearth, 149. 0w iork, John 1iey & Son, Inc., 1950. p 769.U57.
2. i'avis, a1vi 1etor', ed. tar4book or applied hdrau].ic. 2cl ed. New York, McC'raw'-1ll ?ook Compeny, Inc. 1952. 1272 p.
3* Gottath*lk, L. C. Siltink; of etock ponds in land utilizíitio project area SD-.LU2 Pierre, South Dakota. a8h1nCton, D.C. , 1948. 15 p. (!J.s.
Departnen t of Ar'iculture. Soil Conservati on service. Special report o. 9)
4* JenkIns, John E., Chtrle E, Moak and :aniel A. Okun. Sedi.rneitaton in reservoirs th tho Southeaat. Journal of the sanitary FxigLneerin div s ion, Wooeediriga ot tho American Socio tr of Civil }i:er3 S6(3A4) :57O, July 1960.
5. Li81oy, flay . . , Jr. , and Frsnzini H. Joseph. 4;1ement s of Hydraulic gieer1 n, N ow York, Mcraw-i11 i3ook Company, Inc. 1955. &32 e
6. flouse, .urter. Elemertary Mechanics of iluids. ew York, John i1oy and Sons, Inc. l)59. 376 p.
7. Stevens, A. C. The s:it prob1e. TransactIons. American Society of Civil Lninoers lO1:2O7'2C 8. 1936.
3. Srar of roaervoir sedimorttation curveys nade in the United tat.en throu 1053. D.C., 1957. 47 p.
(cy , Federal Inter.Aency
flivez' Basin Con:ittee. adirnontatiori Bulletin o. 6)
9. Taylor, W, Doe.d. Fimdueuta1s of Soil Mechsnioa. i. ow York, John Wiley end Sons, Inc. 1958. 700 p.
s?
lo. Tennessee Valley Autnoritl et . A study of methods used i moasureertt anranaiysis ol' editînt loada In streams. Iowa City, St. ïa1 U. .
gineoring District Sub0ffice ,drau1ic Laboratory, University of Iowa, L41. 203 p. (ieport o. 4)
11. Track, P. Parker. Appiiod Sedincntati an ow York, 3dm Wiley nd Sons, Inc. 1950. 707 p.
12. Twenhofoi, W. í. Principios of Sedimon tat. on. ow Yoric, McCrwrtill ook Compay, Inc. 1939. 610 p.
13. Twsnhoel, W. i. lroatise on Sodi!ter1tation. 2d cd. ßaltirnore, The :: illianis and V lkina Conpany, 1939. 926 p.
14. Vennard, Johzì K. 1ene.tary Fluid Mechanics. 3d ed. New York, John V1ley and Sons, Inc., 1D58. 401 p.
15, Witzig, J. i3ernard. Sedimentation in resrvoi4'a. Transactio :8 of the American Society of Civil Ergineers 100:1047-1106. 1944.
3e
APZE DIX
39
Illustrative example of calculations
(from Ocoee :o. 3 Reservoir)
Proposed metìod
= 100[i.(1_)r.] (from p. 26)
y., from length of record 2.9 yrs 0.0422
Total storage loss percents in O yrs, L3
l00[1_(l_X)8] : 29.2S
VJitzigts method and Brownts iitiiOd
L\SR I (SR)G*83 (from p. 22)
_EQ5 CL (Irom p. 20)
Upper limit, tSR 0.00345 (l2iOO2) 0.89
Annual sediment 0.89 x 263 234 acre-ft
From Fiç.ire 4, page 21, for C/W 24.2, usina upper curve,
0L 2 93x234 : 1.812 12,5
118 1.612 x 8 l4.5
GottschalkT method
E : 93%
s = 0.0522C.0.0027A.0.2681T-l.7974 (from p. 23)
8 yrs, S : 0.0522x12,002.0.0027x168,500.0.2681x8-l.7974
= 1081.35 Acre-ft
L8 : 1081,35x100 9.()3% 12 , 002
